[R] aggregate months to years

[Henrique Dallazuanna]

Try this:

aggregate(ex$FREQ, list(Year =  substr(ex$DATE, 1, 4)), sum)

or

aggregate(ex$FREQ, list(Year = format(as.Date(ex$DATE), "%Y")), sum)



On Mon, Jul 14, 2008 at 9:37 AM, Oehler, Friderike (AGPP)
<Friderike.Oehler at fao.org> wrote:
> Many thanks for the recent answers to my question about pattern recognition.
> The hint to "grep" and the "pattern" argument brought me a big deal forward.
>
> # Now, I have a data frame:
>
> DATE <- c("1930-01-01", "1930-01-01", "1930-02-01", "1931-01-01",
> "1931-02-01", "1931-03-01") # almost all months until "1999-12-01". Day is
> always 01, the same months actually occur several times.
> FREQ <- rep(1,6)
> ex<- data.frame(DATE,FREQ)
>
> # I can aggregate it like this:
>
> ex <- tapply(ex$FREQ, ex$DATE, sum)
>
> # or use"grep" to extract a single year:
> # ex[grep(pattern="^1931", ex$DATE),]
>
> # But how can I aggregate the years such that a barplot would show me the
> FREQ per year and not per month?
>
> barplot(as.vector(ex))
>
> # Sorry for the bad example, of course my data.frame is much bigger and the
> barplot gives me a nice monthly time series of events, but I really only want
> the occurrences per year, not per month.
>
> Grateful for your advice!
> Friderike
>
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>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O